1. Field of the Invention
The present invention relates in general to an apparatus and method for vitrifying inorganic incinerated waste with the simultaneous destruction of any organic hazardous components, and in particular, is directed to vitrification of the inorganic elements present in the ash of the incineration process, metals or metal fractions, to allow safe disposal in landfills in a nonleachable, inert form. Also, the present invention is directed to an apparatus and method for efficiently destroying RCRA hazardous wastes containing any combination of organic and inorganic constituents while converting the inorganic constituents to an inert, nonleachable vitreous slag.
2. Description of the Related Art
Improved disposal and treatment methods are needed to deal with the growing quantities of hazardous waste produced by various U.S. industries. There is an immediate concern to clean up hazardous waste sites resulting from years of uncontrolled dumping. This concern has been manifested in the passage of Federal laws regulating hazardous waste. The Resource Conservation and Recovery Act of 1976 (RCRA) provided for "cradle to grave" controls in the storage, transport, treatment, and disposal of hazardous waste. The Toxic Substances Control Act (TSCA) in 1979 prohibited the further manufacture of polychlorinated biphenyls (PCBs). The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980 addressed the problem of clean-up of the uncontrolled waste sites with the establishment of a national fund or superfund. More recently in 1986 the Superfund Amendments and Reauthorization Act (SARA) expanded the provisions and funding in such clean-up projects. The impact of these laws affects all of industry and eventually consumers in waste management practices.
While many incineration processes have demonstrated acceptable organics destruction efficiencies as required by 40 CFR 264.343, they still produce unacceptable levels of leachable hazardous inorganics in the fly ash and bottom ash. These ash streams containing metals or metal fractions require additional treatment and/or disposal in Resource Conservation and Recovery Act (RCRA) qualified sites.
Metals such as arsenic, barium, beryllium, chromium, cadmium, lead, mercury, nickel, and zinc are of concern in waste incineration. Even though incineration changes the form of metal fractions in waste streams, the metals are not destroyed, but are emitted in the combustion gases as particles or vapors essentially in the same total quantity as the input. The metals may also be emitted with dry bottom ash and collected fly ash which when disposed in landfills have been shown to leach their metal content into surrounding earth and possibly into drinking water sources. As a result, these metal emissions have a potentially adverse impact on the environment and human health.
An apparatus and method are needed which not only destroy the organic part of hazardous waste, but also convert the inorganic components to a relatively inert form.
Various vitrification processes are known for safe disposal of radioactive waste material as is reflected in U.S. Pat. Nos. 3,321,409; 4,020,004; 4,297,304; 4,376,070; and 4,424,149. U.S. Pat. No. 4,666,490 issued to Drake teaches a vitrification process for treatment of nonradioactive hazardous waste materials in an aqueous stream to produce nonleachable glass matrices suitable for landfill disposal. This reference recognizes the problem of loss of toxic vapor to the atmosphere and provides a tight enclosure to contain the vapors evolved in the heat treating environment. However, this process is limited in only being able to treat small quantities of hazardous organic materials.
A one-step process of incineration and glassification using a high-temperature glass-melting furnace to destroy organics and encapsulate heavy metals is described in an article titled "Hazardous Waste: Where to Put It? Where Will It Go?" in Mechanical Engineering magazine, September, 1988, pgs. 70-75. A feeding technique introduces waste materials below the surface of a molten glass pool. The melter operates at a temperature of more than 1150.degree. C. to destroy the organic material while the residual ash is dissolved in the pool of molten glass. The off-gas undergoes an effluent treatment system to remove and neutralize acidic gases generated from the process.
Neither of these prior art approaches recovers the heat from the combustion gases or utilizes existing emission control technology in commercial boiler systems to make safe waste disposal and cleanup applications economically feasible or attractive.
A cyclone combustor or furnace is a high-temperature furnace known in the boiler art to completely destroy combustibles in the fuel while melting the ash into a liquid slag. Fuel is introduced into the burner end of the cyclone furnace with primary air entering the burner tangentially. Secondary air is admitted tangentially at the roof of the cyclone barrel and imparts further centrifugal action to the fuel particles. A small amount of air, tertiary air, is also admitted at the center of the burner. FIG. 1 is a sectional view of a cyclone combustor or furnace. Combustibles in the fuel are burned at heat release rates greater than 450,000 Btu/cu ft, hr. and gas temperatures exceeding 3,000.degree. F. are developed. The incoming fuel particles are thrown to the walls of the cyclone by centrifugal force, held in the slag and scrubbed by high-velocity secondary air. The design of the cyclone furnace is such that the heat release is high and the heat absorption is low.
While it is known to use cyclone furnaces in the manufacture of glass, in general, the use of cyclone furnaces is not readily accepted in the industry since they generate high nitrogen oxides (NO.sub.x) emissions which are an unsuitable pollutant.
In addition, except where natural gas is used, other fuels such as oil and coal have potential of creating unburned carbon which enters the glass matrix and is aesthetically unsuitable for general glass manufacture. For purposes described here such aesthetic defects are of little consequence. Moreover, due to the high temperatures generated in a cyclone furnace, the inorganic waste materials have a tendency to vaporize into the flue gas where they exit into the atmosphere adding to pollution.
Thus, there is a need in the industry for an apparatus and method that provides for the incineration of various types of waste material both organic and inorganic with vitrification of the inorganic elements including the heavy metals generated therefrom. A nonleachable, inert form of this portion of the waste is necessary to allow for disposal in a conventional landfill with no adverse impact on public health and the environment. Similarly, the apparatus and method must not contribute to the overall pollution problem by substituting one pollutant for another.
Further, there is a need for this technology to make waste disposal and cleanup of existing hazardous waste sites economically possible and energy efficient.